Abstract: Planar, integrated, optical air-clad waveguide and method for the manufacture hereof. The air-clad waveguide consists of a thick central part (20) which functions as a wave-guiding core, and thin parts (21, 22) which are connected hereto and serve to support the core and also select which wave types are to be guided through the central part. The thin part is connected to a planar substrate (23). In a preferred embodiment, the air-clad waveguide is formed from the substrate by a combination of the removal of surplus material (24) and thermal oxidation (25). With the invention an add/drop-multiplexer is disclosed, which makes it possible to remove or add one or more signals with well-defined centre wavelength. With the invention a non-linear element for the visible wavelengths as well as wavelengths in the infrared range, and a method for the tuning of filters are also disclosed.